Rapidly melting snow has led to flooding across Wisconsin, with high water overtaking dozens of roads, closing schools and causing a sewage overflow in areas served by the Milwaukee Metropolitan Sewerage District, officials said.

Portions of more than 30 highways and roads across Wisconsin were closed Friday morning because of high water, according to the state Department of Transportation.

The high water is the result of snow melting so rapidly that the saturated and still frozen ground can't absorb it.

Schools were closed in Green Bay and Fond du Lac Friday and many bridges in both cities were closed due to high water.

On Thursday evening, Brown County officials ordered a portion of Bellevue evacuated and another neighborhood to shelter in place as floodwaters from rain and melting snow swamped streets with up to 4 feet of water Thursday night.

In Fond du Lac, flooding shut down Johnson Street on both sides of the Fond du Lac River and people were rescued by boat in the area of Arndt Street at Lincoln, Saterlee and Bell streets.

"I can tell you this morning I'm struggling to get across town because I am not going around barricades or through standing water," Fond du Lac emergency management director Bobbi Hicken said Friday morning. "I am seeing a lot of people do this though."

"There is still a lot of standing water on these roadways and we don't know what is underneath that," she said. "it's an extreme inconvenience, but people just need to listen to these barricades; they are there for the public's safety."

In Milwaukee, MMSD said that it started a combined sewer overflow about 5:45 p.m. Thursday. Melting snow taxed the capacity of its two treatment plants for much of the day and filled much of the deep tunnel system.

The overflow means that untreated waste and stormwater is being released into Lake Michigan.

This is Milwaukee's first overflow of the year, according to spokesman Bill Graffin.

Diverting water out of the district's underground storage system reduces the risk of basement sewer backups.

Flood warnings were extended until Saturday morning for a wide swath of the state from Prairie du Chien to Green Bay.

Warm temperatures have resulted in the region's snowpack melting in just a few days rather than gradually.

The high temperature in Rhinelander on Thursday was forecast to be 50 degrees. In Milwaukee, it was forecast to hit 61 degrees on Thursday.

"The main thing is with everything that has melted and is going into the rivers now," said Tim Halbach, a meteorologist at the National Weather Service office in Sullivan. Water levels are "continuing to go up because there is more and more melting to the north coming down these rivers.

"The flooding that we are looking at now is just going to continue to get worse and increase through the weekend," Halbach said.

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An onlooker takes a photo as City of Fond du Lac public works crews clear an ice jam on the Fond du Lac River that caused flooding Thursday, March 14, 2019, near downtown Fond du Lac.(Photo: Mark Hoffman / Milwaukee Journal Sentinel)

Some of the worst flooding was occurring in Fond du Lac where rescue crews had to move residents to higher ground after ice jams contributed to flooding on the Fond du Lac River.

The state DOT traffic management center was closely monitoring the situation statewide, said Lt. Nate Clarke of the Wisconsin State Patrol.

Information about road closings is posted on 511wi.gov. Clarke recommended that anyone traveling by motor vehicle in the state check the site before hitting the road.

There is a growing list of highway closures and restrictions that is changing hourly, according to a posting on the site.

Clarke also warned motorists not to drive around barricades that block access to flooded areas.

Southwest of Madison in Green County, the emergency management office was reporting flooding on numerous roads across the county and along rivers, streams and low-lying areas, according to the weather service.

Flooding is forecast on a number of rivers in southern Wisconsin.(Photo: National Weather Service - Milwaukee/Sullivan office)

Meanwhile, far southeast Wisconsin, including Milwaukee area counties, could see severe thunderstorms Thursday afternoon as a powerful storm system that brought blizzard conditions to the Plains makes its way into the region.

Severe thunderstorms are possible in southeast Wisconsin on Thursday, according to the National Weather Service.(Photo: National Weather Service - Milwaukee/Sullivan office)

"We mainly think wind is going to be the threat with any of these storms if they develop," Halbach said. "It's something we will have to keep an eye on."

The Red Cross said Thursday night that it had opened four shelters — two in Fond du Lac, one in Prairie du Sac and one in Arcadia. A Red Cross spokesman said the group is working with about 150 people.

The Wisconsin Department of Natural Resources also warned that private wells could be contaminated because of weather conditions.

Property owners who see floodwaters "very near or over their wells should assume their drinking water could be contaminated," the DNR said.

Public water systems do not face the same problems because they are designed to keep out contaminants, the agency said.

Separately, the DNR says it's received reports of 11 manure spills so far since Saturday in areas across the state. That's higher than usual, according to spokesman Andrew Savagian.

Spills in these cases generally are reports of manure that's been applied to fields in recent days and has swept into waterways because of flooding, he said.

"It started over the weekend and it's just been building," he said.

The Fond du Lac Reporter contributed to this report. Contact Joe Taschler at (414) 224-2554 or jtaschler@gannett.com. Follow him on Twitter at @JoeTaschler or Facebook at facebook.com/joe.taschler.1.